1. Although the feasibility of ambitious primary access to space using non-conductive, mechanical tethers has seemed to be severely compromised for some time, the interest in tether systems has moved towards less demanding, medium-term, tether applications with small cable diameters. Typical examples are momentum exchange tethers for propellant-less deorbiting of satellites, or for allowing sample return or waste disposal using reentry vehicles deployed from space platforms. Amongst these were ideas for using conductive materials for the cables, and thus employing the electrodynamic effects of a gravity gradient stabilised tether system for the generation of electrical power, or as means for orbit raising or deorbiting of satellites. Carroll [7] proposed a simple deployment-only tether called SEDS (Small Expendable Deployer System) in 1983, and presented, in 1985, a generic guidebook for the analysis of the wide range of tether applications studied to date.
2. The first flight experiments with tethers started in the mid 1960s with the flight of the manned Gemini/Agena tether flight experiments. The first attempt to use a long deployed tether in space was the Tethered Satellite System (TSS) mission. physics and plasma-electrodynamics [4]. Implemented as a first mission with a retrievable tether in July 1992, TSS-1 explored the short deployment of a satellite in the vicinity of the Shuttle over a stable 20 hour period. The mission success was compromised by mechanical problems experienced with the deployer system, severely limiting the length of the deployed tether. However, it still verified some fundamental dynamics issues concerned with short deployment and gravity gradient stabilisation, with implications for longer deployments [4]. This led to TSS-1R in February 1996, which successfully deployed to 19.7 km (slightly short of the 20.7 km that had been planned). Plasma phenomena were observed with the conductive tether used and showed that currents significantly in excess of numerical predictions could be collected [4].
3. Dynamic analysis was one of the goals of the OEDIPUS-C flight in November 1995, and this system utilised two fore and aft payloads to implement and demonstrate spin stabilisation by means of the so-called Tether Dynamics Experiment (TDE) [4]. The dynamics of spinning tethered twobody 'dumb-bell' systems have received considerable literature attention and this experiment provided valuable in-service tether force data and payload nutation responses within the time domain. Another notable mission was the Tether Physics and Survivability Experiment (TiPS) based on two identical end-bodies (Ralph and Norton) connected together by a 4 km insulating tether. TiPS was ejected from the host spacecraft in June 1996 and the objectives were to investigate long term orbit and attitude dynamics and survivability. This flight provided data which suggested that reasonable longterm survivability could be achievable and that predicted stabilisations of small angle libration can take place [4]. 3. Mechanical Tethers